aureooms/js-fingertree

import assert from 'assert';

import {One, Two} from '../../1-digit/index.js';
import {Empty, Single, Deep} from '../../3-tree/index.js';
import {cache} from '../measure/index.js';

export function _from_small_list(M, list) {
    assert(Number.isInteger(list.length) && list.length >= 0 && list.length <= 3);
    switch (list.length) {
        case 0: {
            return new Empty(M);
        }

        case 1: {
            return new Single(M, list[0]);
        }

        case 2: {
            return new Deep(
                M,
                new One(list[0]),
                new Empty(cache(M)),
                new One(list[1]),
            );
        }

        default: {
            return new Deep(
                M,
                new Two(list[0], list[1]),
                new Empty(cache(M)),
                new One(list[2]),
            );
        }
    }
}